A few months ago I bought a Dell 4700 off of a friend for $30. It worked great up until a few weeks ago. Everything was normal, I turned it off, but then the next day it would not turn on. Instead of the two normal green lights in the front, there was one orange one. Not blinking. I tried removing cards, RAM, CD and DVD Drives, and even replacing the hard drive. Nothing worked. I now believe it is either the motherboard or power supply causing trouble, but as much as I would like to, I barely have enough money for one. So I really need to know what's wrong before I spend any money. Any ideas?

When you don't want to go out and just purchase a new Power Supply, to test
I've actually borrowed a Power Supply from a working computer and tested with that

Power Supply replacement guide here: http://support.dell.com/support/edocs/SYSTEMS/dim4700/sm/parts.htm#wp1055681

Take out the ram hdd, cd and dvd-r's keep your monitor mouse and key board, and go throw everything else off a cliff. It might not sound productive, but due to it being a dell, which are designed, different so you have to buy direct from dell, whose parts are mostly unreliable in my experience. A new mb processor chasis and power supply can probably be purchased for 200$ the rest of the parts you removed can be used to build a system.

I don't think you understood, I don't need to rebuild the system, just replace 1 non-working part.

Anyway, it was the power supply. I used your tip and plugged in another power supply and it worked just fine. Found a new one, same as the one inside, for $30.

Thanks for the update :grinthumb